This invention pertains generally to agricultural apparatus, and more specifically to equipment which is adapted to cut grasses and other upstanding crops by means of a plurality of adjacent rotary cutter elements.
With particular reference to the mowing of grass by means of plural or ganged cutter assemblies, it is usually desired and generally required that the plural cutting means of the machine cut the grass uniformly at a single selected length. When this is accomplished by means of a plurality of side-by-side cutters rotating about adjacent vertical axes, it is a simple enough task to construct or adjust the mower so that the cutting blades are all rotating at the same desired height relative to the ground. A problem exists, however, with respect to ensuring the cutting of the grass between adjacent rotary cutters, since measures must be taken to preclude collisions between adjacent cutters where they are mounted so as to describe overlapping circles of rotation.
One solution to this problem is to mount adjacent rotary cutters in non-overlapping relationship but with the vertical axes of rotation arranged in a line that is askew with respect to the direction of travel of the cutting machine over the field or other area to be cut, so that while the actual circles of rotation described by adjacent rotary cutters do not overlap, the paths cut by such adjacent cutters overlap, to effect a continuous and smooth cutting operation. However, in many applications this structural arrangement is undesirable, it being preferable to arrange the cutters such that the several vertical axes of rotation are in alignment athwart of and substantially perpendicular to the direction of motion of the machinery relative to the ground.
Where a plurality of cutters is mounted as just described, it has become common practice to overlap the cutting circles of adjacent cutters to ensure continuous cutting, but it is then necessary to establish and carefully maintain the relative phasing of the rotation of the several cutters so as to prevent adjacent cutters from striking each other, as would be the case were adjacent cutters to pass through the area of overlap at the same time.
The most common form of rotary cutter constitutes a blade holder in the form of a pair of symmetrically opposed arms extending radially outward from the vertical rotary shaft to which they are attached, with opposed cutting blades being mounted at the outer ends of the respective arms. With adjacent overlapped rotary cutters of this type, it is necessary to phase adjacent rotors such that the cutter blades pass through the area of overlap substantially ninety degrees apart, and it becomes obligatory to maintain this relative rotational relationship rather closely, since such ninety-degree relationship does not allow much margin for error or change before blade interference occurs. From this standpoint, it would be apparent that the ideal rotary drive system would be quite rigid, permitting little play, slack or backlash. However, other conflicting realities of the mowing art call for a rotary drive system with at least some of the elements thereof being capable of yielding at times.
Where the rotary drive system between the power source and the several rotary cutters is substantially rigid or non-yielding, considerable damage can occur in the gear boxes, the drive shafts or in the cutter assemblies themselves, when a cutter "scalps" the ground on uneven terrain or strikes a hard object lying on the ground. Since accidents of this type occur with some frequency and are difficult to avoid during a mowing operation, the machines of the prior art have in some instances been provided with rotary drive shafts capable of yielding to unexpected forces. More specifically, some machines have flexible rotary drive shafts extending between adjacent ones of a series of in-line gear boxes, whereby temporary stoppage of a rotary blade can result in "wind-up" or torsional twisting of a flexible drive shaft, preventing structural damage to the parts as a result of the stoppage, but at the expense of a positional error or rotational misalignment of up to sixty degrees over the length of the flexible shaft. Clearly, the aforementioned ninety-degree relationship between blades of adjacent cutters passing through an area of overlap cannot tolerate the resultant misalignment of the rotors, since the blades on such adjacent rotors will collide, with resultant damage to the blades and perhaps to the drive mechanism.